Planetary gear train of automatic transmission for vehicle

ABSTRACT

A planetary gear train may include input and output shafts, first to fourth planetary gear sets respectively having first to third, fourth to sixth, seventh to ninth, and tenth to twelfth elements, a first shaft connected to the fifth and eighth elements, and selectively connectable to the input shaft, a second shaft connected to the tenth element, and selectively connectable to the input shaft, a third shaft connected to the ninth element the output shaft, a fourth shaft connected to the third and twelfth elements, a fifth shaft connected to the seventh and eleventh elements, and a plurality of shafts each selectively connecting a corresponding element to a transmission housing, the corresponding element being an element of the first and second planetary gear sets which is not interconnected.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2017-0135819 filed on Oct. 19, 2017, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an automatic transmission for avehicle.

Description of Related Art

Research on realizing more shift-stages of an automatic transmission areundertaken to achieve enhancement of fuel consumption and betterdrivability, and recently, increase of oil price is triggering a hardcompetition in enhancing fuel consumption of a vehicle.

In this sense, research on an engine has been undertaken to achieveweight reduction and to enhance fuel consumption by so-called downsizingresearch on an automatic transmission has been performed tosimultaneously provide better drivability and fuel consumption byachieving more shift stages.

To achieve more shift stages for an automatic transmission, the numberof parts is typically increased, which may deteriorate installability,production cost, weight and/or power flow efficiency.

Therefore, to maximally enhance fuel consumption of an automatictransmission having more shift stages, it is important for betterefficiency to be derived by fewer number of parts.

In this respect, an eight-speed automatic transmission has been recentlyintroduced, and a planetary gear train for an automatic transmissionfacilitating more shift stages is under investigation.

An automatic transmission of eight or more shift-stages typicallyincludes three to four planetary gear sets and five to seven engagementelements (frictional elements), and may easily become lengthy,deteriorating installability.

In this regard, disposing planetary gear sets in parallel or employingdog clutches instead of wet-type control elements is sometimesattempted. However, such an arrangement may not be widely applicable,and using dog clutches may easily deteriorate shift-feel.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and may not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission for a vehiclefacilitating at least ten forward speeds, providing better performanceand fuel efficiency of a vehicle.

A planetary gear train according to an exemplary embodiment of thepresent invention may include an input shaft receiving an engine torque,an output shaft outputting a shifted torque, a first planetary gear sethaving first, second and third rotation elements, a second planetarygear set having fourth, fifth, and sixth rotation elements, a thirdplanetary gear set having seventh, eighth, and ninth rotation elements,and a fourth planetary gear set having tenth, eleventh, and twelfthrotation elements. An exemplary planetary gear train may further includea first shaft fixedly connected to the fifth rotation element and theeighth rotation element, and selectively connectable to the input shaft,a second shaft fixedly connected to the tenth rotation element, andselectively connectable to the input shaft, a third shaft fixedlyconnected to the ninth rotation element, and fixedly connected to theoutput shaft, a fourth shaft fixedly connected to the third rotationelement and the twelfth rotation element, a fifth shaft fixedlyconnected to the seventh rotation element and the eleventh rotationelement, and a plurality of shafts each selectively connecting acorresponding element to the transmission housing, the correspondingelement being a rotation element of the first and second planetary gearsets which is not fixedly interconnected.

The plurality of shafts may include a sixth shaft fixedly connected tothe first rotation element and the fourth rotation element andselectively connectable to the transmission housing, and a seventh shaftfixedly connected to the second rotation element and the sixth rotationelement and selectively connectable to the transmission housing. Theinput shaft and the first shaft, the input shaft and the second shaft,the fifth shaft and the seventh shaft, and the second shaft and theseventh shaft may be selectively interconnected to each otherrespectively.

The exemplary planetary gear train may further include four clutcheseach selectively connecting a corresponding pair among the input shaft,the output shaft, and the first to seventh shafts, and two brakesselectively connecting the sixth shaft and the seventh shaft to thetransmission housing respectively.

The four clutches may include a first clutch disposed between the inputshaft and the first shaft, a second clutch disposed between the inputshaft and the second shaft, a third clutch disposed between the fifthshaft and the seventh shaft, and a fourth clutch disposed between thesecond shaft and the seventh shaft. The two brakes may include a firstbrake disposed between the sixth shaft and the transmission housing, anda second brake disposed between the seventh shaft and the transmissionhousing.

The first planetary gear set may be a single pinion planetary gear sethaving a first sun gear, a first planet carrier, and a first ring gearas the first, second and third rotation elements. The second planetarygear set may be a single pinion planetary gear set having a second sungear, a second planet carrier, and a second ring gear as the fourth,fifth, and sixth rotation elements. The third planetary gear set may bea single pinion planetary gear set having a third sun gear, a thirdplanet carrier, and a third ring gear as the seventh, eighth, and ninthrotation elements. The fourth planetary gear set may be a single pinionplanetary gear set having a fourth sun gear, a fourth planet carrier,and a fourth ring gear as the tenth, eleventh, and twelfth rotationelements.

The first, second, third and fourth planetary gear sets may be disposedin the order of the third, fourth, second, and first planetary gear setsfrom an engine side.

A planetary gear train according to an exemplary embodiment of thepresent invention may realize at least ten forward speeds and onereverse speed by combination of four planetary gear sets of simpleplanetary gear sets together with six engagement element.

Furthermore, a planetary gear train according to an exemplary embodimentof the present invention may improve driving stability by realizingshift-stages appropriate for rotation speed of an engine due tomulti-stages of an automatic transmission.

Furthermore, a planetary gear train according to an exemplary embodimentof the present invention may maximize engine driving efficiency bymulti-stages of an automatic transmission, and may improve powerdelivery performance and fuel consumption.

Furthermore, effects that can be obtained or expected from exemplaryembodiments of the present invention are directly or suggestivelydescribed in the following detailed description. That is, variouseffects expected from exemplary embodiments of the present inventionwill be described in the following detailed description.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a planetary gear train according to anexemplary embodiment of the present invention.

FIG. 2 is an operational chart for respective control elements atrespective shift-stages applicable to a planetary gear train accordingto an exemplary embodiment of the present invention.

It may be understood that the appended drawings are not necessarily toscale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and the shapes will be determined in part by the particularly intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Hereinafter, an exemplary embodiment of the present invention will bedescribed more specifically with reference to drawings.

The drawings and description are to be regarded as illustrative innature and not restrictive, and like reference numerals designate likeelements throughout the specification.

In the following description, dividing names of components into first,second, and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited.

FIG. 1 is a schematic diagram of a planetary gear train according to anexemplary embodiment of the present invention.

Referring to FIG. 1, a planetary gear train according to an exemplaryembodiment of the present invention may include first, second, third andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on a sameaxis, an input shaft IS, an output shaft OS, seven shafts TM1 to TM7interconnecting rotation elements of the first, second, third and fourthplanetary gear sets PG1, PG2, PG3, and PG4, engagement elements of fourclutches C1 to C4 and two brakes B1 and B2, and a transmission housingH.

Torque input from the input shaft IS is shifted by cooperative operationof the first, second, third and fourth planetary gear sets PG1, PG2,PG3, and PG4, and then output through the output shaft OS.

In an exemplary embodiment of the present invention, the planetary gearsets are disposed in the order of the third, fourth, second, and firstplanetary gear sets PG3, PG4, PG2, and PG1, from an engine side.

The input shaft IS is an input member and may receive a torque from acrankshaft of an engine through a torque converter.

The output shaft OS is an output element disposed on a same axis withthe input shaft IS, and outputs a shifted driving torque to a driveshaftthrough a differential apparatus.

The first planetary gear set PG1 is a single pinion planetary gear set,and may include a first sun gear S1, a first planet carrier PCIrotatably supporting a plurality of first pinion gears P1 externallygear-meshed with the first sun gear S1, and a first ring gear R1internally gear-meshed with the plurality of first pinion gears P1engaged with the first sun gear SI. The first sun gear S1 acts as afirst rotation element N1, the first planet carrier PCI acts as a secondrotation element N2, and the first ring gear R1 acts as a third rotationelement N3.

The second planetary gear set PG2 is a single pinion planetary gear set,and may include a second sun gear S2, a second planet carrier PC2rotatably supporting a plurality of second pinion gears P2 externallygear-meshed with the second sun gear S2, and a second ring gear R2internally gear-meshed with the plurality of second pinion gears P2engaged with the second sun gear S2. The second sun gear S2 acts as afourth rotation element N4, the second planet carrier PC2 acts as afifth rotation element N5, and the second ring gear R2 acts as a sixthrotation element N6.

The third planetary gear set PG3 is a single pinion planetary gear set,and may include a third sun gear S3, a third planet carrier PC3rotatably supporting a plurality of third pinion gears P3 externallygear-meshed with the third sun gear S3, and a third ring gear R3internally gear-meshed with the plurality of third pinion gears P3engaged with the third sun gear S3. The third sun gear S3 acts as aseventh rotation element N7, the third planet carrier PC3 acts as aneighth rotation element N8, and the third ring gear R3 acts as a ninthrotation element N9.

The fourth planetary gear set PG4 is a single pinion planetary gear set,and may include a fourth sun gear S4, a fourth planet carrier PC4rotatably supporting a plurality of fourth pinion gears P4 externallygear-meshed with the fourth sun gear S4, and a fourth ring gear R4internally gear-meshed with the plurality of fourth pinion gears P4engaged with the fourth sun gear S4. The fourth sun gear S4 acts as atenth rotation element N10, the fourth planet carrier PC4 acts as aneleventh rotation element N11, and the fourth ring gear R4 acts as atwelfth rotation element N12

In the first, second, third and fourth planetary gear sets PG1, PG2,PG3, and PG4, the first rotation element N1 is fixedly connected to thefourth rotation element N4, the second rotation element N2 is fixedlyconnected to the sixth rotation element N6, the third rotation elementN3 is fixedly connected to the twelfth rotation element N12, the fifthrotation element N5 is fixedly connected to the eighth rotation elementN8, the seventh rotation element N7 is fixedly connected to the eleventhrotation element N11, and seven shafts TM1 to TM7 are formed.

The seven shafts TM1 to TM7 are hereinafter described more specifically.

The first shaft TM1 is fixedly connected to fifth rotation element N5(second planet carrier PC2) and eighth rotation element N8 (third planetcarrier PC3), and selectively connectable to the input shaft ISselectively acting as an input element.

The second shaft TM2 is fixedly connected to the tenth rotation elementN10 (fourth sun gear S4), and selectively connectable to the input shaftIS selectively acting as an input element.

The third shaft TM3 is fixedly connected to the ninth rotation elementN9 (third ring gear R3), and fixedly connected to the output shaft OSalways acting as an output element.

The fourth shaft TM4 is fixedly connected to third rotation element N3(first ring gear R1) and twelfth rotation element N12 (fourth ring gearR4).

The fifth shaft TM5 is fixedly connected to seventh rotation element N7(third sun gear S3) and eleventh rotation element N11 (fourth planetcarrier PC4).

The sixth shaft TM6 is fixedly connected to first rotation element N1(first sun gear S1) and fourth rotation element N4 (second sun gear S2).

The seventh shaft TM7 is fixedly connected to second rotation element N2(first planet carrier PC1) and sixth rotation element N6 (second ringgear R2).

Each of the seven shafts TM1 to TM7 may be a rotation member thatfixedly interconnects the input and output shafts and rotation elementsof the planetary gear sets PG1, PG2, PG3, and PG4, or may be a rotationmember that selectively interconnects a rotation element to thetransmission housing H, or may be a fixed member fixed to thetransmission housing H.

In the disclosure, when two or more members are described to be “fixedlyconnected”, where the member may be any of a shaft, an input shaft, anoutput shaft, a rotation member, and a transmission housing, it meansthat the fixedly connected members always rotate at a same speed.

When two or more members are described to be “selectively connectable”by an engagement element, it means that the selectively connectablemembers rotates separately when the engagement element is not engaged,and rotates at a same speed when the engagement element is engaged. Itmay be understood that in the case that a member is “selectivelyconnectable” with a transmission housing by an engagement element, themember may be stationary when the engagement element is engaged.

The first shaft TM1 is selectively connectable to the input shaft IS,the second shaft TM2 is selectively connectable to the input shaft IS,the fifth shaft TM5 is selectively connectable to the seventh shaft TM7,and the second shaft TM2 is selectively connectable to the seventh shaftTM7.

The sixth shaft TM6 and the seventh shaft TM7 are selectivelyconnectable to the transmission housing H, selectively acting as fixedelements respectively.

The engagement elements of four clutches C1, C2, C3, and C4 are disposedbetween the seven shafts TM1 to TM7, the input shaft IS, and the outputshaft OS, to form selective connections.

The seven shafts TM1 to TM7 may be selectively connectable to thetransmission housing H, by control elements of two brakes B1 and B2.

The six engagement elements of the four clutches C1 to C4 and the twobrakes B1 and B2 are disposed as follows.

The first clutch C1 is disposed between the input shaft IS and the firstshaft TM1, and selectively connects the input shaft IS and the firstshaft TM1, controlling power delivery therebetween.

The second clutch C2 is disposed between the input shaft IS and thesecond shaft TM2, and selectively connects the input shaft IS and thesecond shaft TM2, controlling power delivery therebetween.

The third clutch C3 is disposed between the fifth shaft TM5 and theseventh shaft TM7, and selectively connects the fifth shaft TM5 and theseventh shaft TM7, controlling power delivery therebetween.

The fourth clutch C4 is disposed between the second shaft TM2 and theseventh shaft TM7, and selectively connects the second shaft TM2 and theseventh shaft TM7, controlling power delivery therebetween.

The first brake B1 is disposed between the sixth shaft TM6 and thetransmission housing H, and selectively connects the sixth shaft TM6 tothe transmission housing H.

The second brake B2 is disposed between the seventh shaft TM7 and thetransmission housing H, and selectively connects the seventh shaft TM7to the transmission housing H.

The engagement elements of the first, second, third and fourth clutchesC1, C2, C3, and C4 and the first and second brakes B1 and B2 may berealized as multi-plate hydraulic pressure friction devices that arefrictionally engaged by hydraulic pressure, however, it may not beunderstood to be limited thereto, since various other configuration thatare electrically controllable may be available.

FIG. 2 is an operational chart for respective control elements atrespective shift-stages applicable to a planetary gear train accordingto an exemplary embodiment of the present invention.

Referring to FIG. 2, a planetary gear train according to an exemplaryembodiment of the present invention realizes shifting between tenforward speeds and one reverse speed by operating three elements amongthe engagement elements of the first, second, third and fourth clutchesC1, C2, C3, and C4 and the first and second brakes B1 and B2.

In the first forward speed D1, the second and fourth clutches C2 and C4and the first brake B1 are simultaneously operated.

As a result, the input shaft IS and the second shaft TM2 are connectedby the operation of the second clutch C2, and the second shaft TM2 andthe seventh shaft TM7 are connected by the operation of the fourthclutch C4. In the present state, a torque is input to the second shaftTM2.

In such a state, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, realizing the first forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the second forward speed D2, the first and fourth clutches C1 and C4and the first brake B1 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the second shaft TM2 and theseventh shaft TM7 are connected by the operation of the fourth clutchC4. In the present state, a torque is input to the first shaft TM1.

In such a state, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, realizing the second forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the third forward speed D3, the first and second clutch C1 and C2 andthe first brake B1 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the input shaft IS and thesecond shaft TM2 are connected by the operation of the second clutch C2.In the present state, a torque is input to the first shaft TM1 and thesecond shaft TM2.

In such a state, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, realizing the third forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the fourth forward speed D4, the first and third clutches C1 and C3and the first brake B1 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the fifth shaft TM5 and theseventh shaft TM7 are connected by the operation of the third clutch C3.In the present state, a torque is input to the first shaft TM1.

In such a state, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, realizing the fourth forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the fifth forward speed D5, the second and third clutches C2 and C3and the first brake B1 are simultaneously operated.

As a result, the input shaft IS and the second shaft TM2 are connectedby the operation of the second clutch C2, and the fifth shaft TM5 andthe seventh shaft TM7 are connected by the operation of the third clutchC3. In the present state, a torque is input to the second shaft TM2.

In such a state, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, realizing the fifth forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the sixth forward speed D6, the first, second and third clutches C1,C2, and C3 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, the input shaft IS and the secondshaft TM2 are connected by the operation of the second clutch C2, andthe fifth shaft TM5 and the seventh shaft TM7 are connected by theoperation of the third clutch C3.

As such, the first, second, third and fourth planetary gear sets PG1,PG2, PG3, and PG4 integrally rotate, and a torque is input to the firstshaft TM1 and the second shaft TM2, realizing the sixth forward speedwhere a torque is output as inputted, and outputting a shifted torque tothe output shaft OS connected to the third shaft TM3.

In the seventh forward speed D7, the second and third clutches C2 and C3and the second brake B2 are simultaneously operated.

As a result, the input shaft IS and the second shaft TM2 are connectedby the operation of the second clutch C2, and the fifth shaft TM5 andthe seventh shaft TM7 are connected by the operation of the third clutchC3. In the present state, a torque is input to the second shaft TM2.

In such a state, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, realizing the seventh forward speedand outputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the eighth forward speed D8, the first and third clutches C1 and C3and the second brake B2 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the fifth shaft TM5 and theseventh shaft TM7 are connected by the operation of the third clutch C3.In the present state, a torque is input to the first shaft TM1.

In such a state, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, realizing the eighth forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the ninth forward speed D9, the first and second clutch C1 and C2 andthe second brake B2 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the input shaft IS and thesecond shaft TM2 are connected by the operation of the second clutch C2.In the present state, a torque is input to the first shaft TM1 and thesecond shaft TM2.

In such a state, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, realizing the ninth forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the tenth forward speed D10, the first and fourth clutches C1 and C4and the second brake B2 are simultaneously operated.

As a result, the input shaft IS and the first shaft TM1 are connected bythe operation of the first clutch C1, and the second shaft TM2 and theseventh shaft TM7 are connected by the operation of the fourth clutchC4. In the present state, a torque is input to the first shaft TM1.

In such a state, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, realizing the tenth forward speed andoutputting a shifted torque to the output shaft OS connected to thethird shaft TM3.

In the reverse speed REV, the second clutch C2 and the first and secondbrakes B1 and B2 are simultaneously operated.

As a result, the input shaft IS and the second shaft TM2 are connectedby the operation of the second clutch C2. In the present state, a torqueis input to the second shaft TM2.

In such a state, the sixth shaft TM6 and seventh shaft TM7 act as fixedelements by the operation of the first and second brakes B1 and B2,realizing the reverse speed and outputting a reverse torque through theoutput shaft OS connected to the third shaft TM3.

As described above, a planetary gear train according to an exemplaryembodiment of the present invention may realize ten forward speeds andone reverse speed by operating the four planetary gear sets PG1, PG2,PG3, and PG4 by controlling the four clutches C1, C2, C3, and C4 and thetwo brakes B1 and B2.

Furthermore, a planetary gear train according to an exemplary embodimentof the present invention may substantially improve driving stability byrealizing shift-stages appropriate for rotation speed of an engine dueto multi-stages of an automatic transmission.

Furthermore, a planetary gear train according to an exemplary embodimentof the present invention may maximize engine driving efficiency bymulti-stages of an automatic transmission, and may improve powerdelivery performance and fuel consumption.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “internal”, “outer”, “up”, “down”,“upper”, “lower”, “upwards”, “downwards”, “front”, “rear”, “back”,“inside”, “outside”, “inwardly”, “outwardly”, “internal”, “external”,“internal”, “outer”, “forwards”, and “backwards” are used to describefeatures of the exemplary embodiments with reference to the positions ofsuch features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described toexplain certain principles of the invention and their practicalapplication, to enable others skilled in the art to make and utilizevarious exemplary embodiments of the present invention, as well asvarious alternatives and modifications thereof. It is intended that thescope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train apparatus of an automatictransmission for a vehicle, comprising: an input shaft receiving anengine torque; an output shaft outputting a shifted torque; a firstplanetary gear set having a first rotation element, a second rotationelement, and a third rotation element; a second planetary gear sethaving a fourth rotation element, a fifth rotation element, and a sixthrotation element; a third planetary gear set having a seventh rotationelement, an eighth rotation element, and a ninth rotation element; afourth planetary gear set having a tenth rotation element, an eleventhrotation element, and a twelfth rotation element; a first shaft fixedlyconnected to the fifth rotation element and the eighth rotation element,and selectively connectable to the input shaft; a second shaft fixedlyconnected to the tenth rotation element, and selectively connectable tothe input shaft; a third shaft fixedly connected to the ninth rotationelement, and fixedly connected to the output shaft; a fourth shaftfixedly connected to the third rotation element and the twelfth rotationelement; a fifth shaft fixedly connected to the seventh rotation elementand the eleventh rotation element; and a plurality of shafts eachselectively connecting a corresponding element to a transmissionhousing, the corresponding element being a rotation element of the firstand second planetary gear sets which is not fixedly interconnected. 2.The planetary gear train apparatus of claim 1, wherein the plurality ofshafts includes: a sixth shaft fixedly connected to the first rotationelement and the fourth rotation element and selectively connectable tothe transmission housing; and a seventh shaft fixedly connected to thesecond rotation element and the sixth rotation element and selectivelyconnectable to the transmission housing, wherein the input shaft isselectively connectable to the first shaft, the input shaft isselectively connectable to the second shaft, the fifth shaft isselectively connectable to the seventh shaft, and the second shaft isselectively connectable to the seventh shaft are selectivelyinterconnected to each other respectively.
 3. The planetary gear trainapparatus of claim 2, further including: four clutches each selectivelyconnecting a corresponding pair among the input shaft, the output shaft,and the first to seventh shafts; and two brakes selectively connectingthe sixth shaft and the seventh shaft to the transmission housingrespectively.
 4. The planetary gear train apparatus of claim 3, whereinthe four clutches comprise: a first clutch mounted between the inputshaft and the first shaft; a second clutch mounted between the inputshaft and the second shaft; a third clutch mounted between the fifthshaft and the seventh shaft; and a fourth clutch mounted between thesecond shaft and the seventh shaft, wherein the two brakes comprise: afirst brake mounted between the sixth shaft and the transmissionhousing; and a second brake mounted between the seventh shaft and thetransmission housing.
 5. The planetary gear train apparatus of claim 1,wherein the first planetary gear set is a single pinion planetary gearset having a first sun gear, a first planet carrier, and a first ringgear as the first rotation element, the second rotation element, and thethird rotation element, the second planetary gear set is a single pinionplanetary gear set having a second sun gear, a second planet carrier,and a second ring gear as the fourth rotation element, the fifthrotation element, and the sixth rotation element, the third planetarygear set is a single pinion planetary gear set having a third sun gear,a third planet carrier, and a third ring gear as the seventh rotationelement, the eighth rotation element, and the ninth rotation element,the fourth planetary gear set is a single pinion planetary gear sethaving a fourth sun gear, a fourth planet carrier, and a fourth ringgear as the tenth rotation element, the eleventh rotation element, andthe twelfth rotation element.
 6. The planetary gear train apparatus ofclaim 1, wherein the first, second, third and fourth planetary gear setsare disposed in an order of the third, fourth, second, and firstplanetary gear sets from an engine side thereof.
 7. A planetary geartrain apparatus of an automatic transmission for a vehicle, comprising:an input shaft receiving an engine torque; an output shaft outputting ashifted torque; a first planetary gear set having a first rotationelement, a second rotation element, and a third rotation element; asecond planetary gear set having a fourth rotation element, a fifthrotation element, and a sixth rotation element; a third planetary gearset having a seventh rotation element, an eighth rotation element, and aninth rotation element; a fourth planetary gear set having a tenthrotation element, an eleventh rotation element, and a twelfth rotationelement, wherein the first rotation element is fixedly connected to thefourth rotation element, and selectively connectable to a transmissionhousing, the second rotation element is fixedly connected to the sixthrotation element, and selectively connectable to the transmissionhousing, the third rotation element is fixedly connected to the twelfthrotation element, the fifth rotation element is fixedly connected to theeighth rotation element, and selectively connectable to the input shaft,the seventh rotation element is fixedly connected to the eleventhrotation element, and selectively connectable to the second rotationelement, the ninth rotation element is fixedly connected to the outputshaft, and the tenth rotation element is are selectively connectable tothe input shaft and the second rotation element, respectively.
 8. Theplanetary gear train apparatus of claim 7, further including: fourclutches each selectively connecting a corresponding pair among theinput shaft, the output shaft, and the first to twelfth rotationelements; and two brakes selectively connecting the first rotationelement and the second rotation element to the transmission housingrespectively.
 9. The planetary gear train apparatus of claim 8, whereinthe four clutches comprise: a first clutch mounted between the inputshaft and the eighth rotation element; a second clutch mounted betweenthe input shaft and the tenth rotation element; a third clutch mountedbetween the second rotation element and the eleventh rotation element;and a fourth clutch mounted between the second rotation element and thetenth rotation element, wherein the two brakes comprise: a first brakemounted between the first rotation element and the transmission housing;and a second brake mounted between the second rotation element and thetransmission housing.
 10. The planetary gear train apparatus of claim 7,wherein the first planetary gear set is a single pinion planetary gearset having a first sun gear, a first planet carrier, and a first ringgear as the first rotation element, the second rotation element, and thethird rotation element, the second planetary gear set is a single pinionplanetary gear set having a second sun gear, a second planet carrier,and a second ring gear as the fourth rotation element, the fifthrotation element, and the sixth rotation element, the third planetarygear set is a single pinion planetary gear set having a third sun gear,a third planet carrier, and a third ring gear as the seventh rotationelement, the eighth rotation element, and the ninth rotation element,the fourth planetary gear set is a single pinion planetary gear sethaving a fourth sun gear, a fourth planet carrier, and a fourth ringgear as the tenth rotation element, the eleventh rotation element, andthe twelfth rotation element.
 11. The planetary gear train apparatus ofclaim 7, wherein the first, second, third and fourth planetary gear setsare disposed in an order of the third, fourth, second, and firstplanetary gear sets from an engine side thereof